A man in a wheelchair eats as he waits to be evacuated from a rebel-held sector of eastern Aleppo, Syria.
Photograph: Abdalrhman Ismail/Reuters

As the green surrender buses trickled out of Aleppo last Wednesday, Bashar al-Assad’s two biggest backers reacted very differently.

Russia, which had brokered the deal with Turkey to allow the refugees to leave, was urging the convoy on towards the countryside, where the first of the city’s final refugees were to be disgorged. Iran, on the other hand, was looking for ways to stop it.

To Moscow, the ceasefire was the pinnacle of Russia’s intervention in Aleppo, a moment when it could mount a new case as a peacemaker, after bombing opposition groups to capitulation for 15 months. To Tehran, allowing remaining civilians and rebel fighters to leave was a potential loss of leverage – at precisely the time that Iranian influence on the battlefield had started to eclipse that of Russia’s.

The divergence marked a seminal moment in the Syrian war; the mutual interest in securing Assad that had brought the two countries together had suddenly given way to a feud about who calls the shots now that the war is nearly won. The Russian air force matters little now. The Iranian revolutionary guards count for more.

Besieged populations have been bargaining chips throughout the six-year conflict, and Iran has played a direct role in turning the fate of cornered opposition communities into political victories that secure Assad and strengthen its own hand.

Allowing the last desperate holdouts of Aleppo to leave, without first seeking terms, was not in the Iranian playbook. And, within hours of Turkey and Russia announcing a deal, Iran had sabotaged it, demanding the lifting of a siege of two Shia villages north of Aleppo, Fua and Kefraya, which had been surrounded by the al-Qaida-inspired Jabhat Fateh al-Sham. It also wanted a trade of prisoners and bodies of slain Hezbollah and Iraqi militants under its tutelage.

Victory in Aleppo matters enormously for both sides, but when the dust settles in Aleppo, it counts for more in Iran

Martin Chulov

Victory in Aleppo matters enormously for both sides, but when the dust finally settles in Aleppo, it counts for more in Iran. Securing Syria’s second city and industrial heart is much less to do with re-establishing state sovereignty than about asserting its own influence and agenda in the strategic heart of the region.

Iranian officials have directly negotiated with the opposition militia, Ahrar al-Sham, about the fate of the battered opposition-held town of Zabadani, west of Damascus. Iran proposed a swap of the town’s Sunnis, who would be sent to Idlib province, for the residents of Fua and Kefraya, who would in turn be relocated to Zabadani.

“The Iranians want no Sunnis between Damascus and the Lebanese border,” said one senior Lebanese official yesterday. “There is a very clear plan to change the sectarian tapestry of the border.”

In the Damascus suburb of Darayya, where opposition communities surrendered in August, and accepted being flown to Idlib, 300 Shia families from Iraq have moved in. Further to the west, near the Zainab shrine, Iran has bought substantial numbers of properties, and also sponsored the arrival of Shia families, securing the area as a bridgehead before Zabadani.

Securing corridors of influence with Shia communities marks, potentially, Iran’s most assertive moment since the Islamic revolution of 1979, after which Tehran’s proxies have gradually projected its influence, through Hezbollah, through the US invasion of Iraq – which switched political power from Sunnis to Shias – and now through the chaos of Syria.

Russia’s goals have been less about ideology, and more about realpolitik. Vladimir Putin now has a renewed stake in the region, at the expense of the US, which he believes abdicated a decades-long role under Barack Obama, and which Donald Trump has little interest in reclaiming. Russian influence is likely back in the Middle East to stay. But, as America found out, it will be checked by the fervour of an ascendant regional heavyweight.